The present invention relates to power actuated tools and more particularly to explosively actuated tools for driving a fastener such as a pin into a substrate such as concrete or steel.
Explosively actuated tools for driving a fastener such as a pin into a substrate such as concrete or steel conventionally comprise a driving piston which is driven forwardly along the barrel of the tool upon detonation of an explosive charge to drive into the substrate a fastener within the forward end of the barrel. After the firing stroke has been completed, the driving piston is within the forward end of the barrel and appropriate action must be taken to reset the piston into a rear position within the barrel in preparation for the next driving stroke. This may be achieved by a manual action by the operator. One method of manually resetting the piston which is widely used in practice involves the operator drawing the barrel forwardly from the housing of the tool while the piston is restrained so that the piston lies within a rear part of the barrel which is then retracted manually back into the housing.
There have been proposals for automatic or semi-automatic resetting of the piston. One such proposal involves the use of the explosive gas generated on firing the tool to drive the piston back into its rear position within the barrel after firing. Such a system can however lead to safety problems as the ducting of the explosive gas to a piston return mechanism can result in accumulation of unburnt explosive powder within the mechanism. Further, the problem arising from unburnt residues may be compounded if the tool is not used shortly after resetting of the piston and is subject to rough handling or vibration, for example by being transported on the floor of a truck whereby the previously reset piston can move out of its predetermined rear position leading to loss of power and possible generation of increasing amounts of unburnt residue at the next firing action.
Explosively actuated fastener driving tools of the type to which the present invention relates conventionally comprise a safety mechanism whereby to fire the tool the firing mechanism must be cocked by pushing the forward end of the barrel against the substrate, this causing the barrel to retract through a limited distance into the housing of the tool and this movement, in turn, cocks the tool and enables firing of the tool. This safety mechanism is designed to ensure that the tool can only be fired in its operative position pressed against the substrate and the cocking mechanism responsive to the retraction of the barrel within the tool housing is well known per se to those skilled in this art. The present invention utilises the relative movement between the barrel and housing which occurs when the barrel is pressed against the substrate on cocking also to effect resetting of the piston into its rear position.
According to the present invention there is provided a power actuated tool for driving a fastener into a substrate such as steel or concrete, said tool comprising a housing, a barrel mounted within the housing, and a piston displaceable within the barrel upon firing of the tool to drive a fastener from the forward end of the barrel into the substrate, at least a forward end of the barrel being mounted for axial movement relative to the housing whereby firing of the tool requires the forward end of the barrel to be pressed against the substrate to cause retraction of the forward end of the barrel relative to the tool housing, said tool further comprising piston resetting means responsive to retraction of the forward end of the barrel relative to the tool housing prior to firing the tool to cause displacement of the piston rearwardly relative to the barrel in preparation for that firing. Advantageously, said piston resetting means comprises means engagable with the piston in its forward position, an energy source charged with energy by the relative displacement of the forward end of the barrel inwardly relative to the housing, and means for releasing energy stored in said energy source whereby said stored energy drives the engagement means rearwardly to thereby drive the piston rearwardly relative to the barrel.
In a preferred embodiment the energy source comprises a spring in which potential energy is stored by the relative displacement between the barrel and housing and said potential energy is suddenly released to drive the piston rearwardly. Preferably the spring is a coil spring although other forms of spring such as an elastomeric spring or gas spring may alternatively be used.
In a preferred embodiment the engagement means is operative to releasably grip the piston and sudden release of the spring energy imparts a certain rearwards movement to the gripping means to impart a sudden thrust to the piston, the gripping means then releasing from gripping engagement with the piston at the end of rearwards movement of the gripping means whereby the momentum of the piston propels it further rearwardly into its rearmost position in the barrel.
Preferably piston retention means are provided to retain the piston in its rearmost position prior to firing the tool, said retention means acting in response to rebound of the piston from its rearmost position as a result of the sudden thrust used to effect resetting.
Further according to the invention, there is provided a power actuated tool for driving a fastener into a substrate such as steel or concrete, said tool comprising a housing, a barrel mounted within the housing, and a piston displaceable within the barrel upon firing of the tool to drive a fastener from the forward end of the barrel into the substrate, at least a forward end of the barrel being mounted for axial movement relative to the housing such that cocking of the tool to effect firing requires the forward end of the barrel to be pressed against the substrate to cause retraction of the forward end of the barrel relative to the tool housing, said tool further comprising piston resetting means responsive to cocking of the tool to reset the piston to the rear of the barrel in preparation for the firing, said resetting means comprising a spring-loaded gripper device energised during cocking to grip the piston and thrust the piston rearwardly.
Still further according to the invention, there is provided a power actuated tool for driving a fastener such as a pin into a substrate such as steel or concrete, said tool comprising a driving piston which is driven forwardly within a barrel of the tool upon firing, and means for automatically resetting the piston to the rear of the barrel in response to cocking of the tool prior to the subsequent firing.